Three-bucket quadrature phase stepping in a shearing speckle interferometer

Phase stepping algorithms are mostly based on three or more interferograms that can either be acquired sequentially, involving some temporal phase stepping mechanism, or in parallel. When a phase step is applied between acquisitions, object phase changes may cause phase errors when calculating phase. A new system that allows the object to change in between arbitrary temporal phase steps is proposed. It comprises a relatively simple polarization based two-channel speckle interferometer that acquires two π/2 phase stepped interferograms simultaneously with a single camera. This quadrature pair is phase stepped with a temporal phase stepping system that is also polarization based. Simulations and experimental results are presented that illustrate the improvements achieved with quadrature phase stepping compared to results obtained with the two-channel speckle interferometer operated without additional temporal phase stepping.